Tobacco control in dental practices is both important and under-used, in part because not enough is known about effective methods for translating tobacco counseling guidelines into practice. We propose a randomized controlled trial (RCT) to test an interactive, multimodal intervention designed to increase tobacco cessation counseling in dental practices. Methods: Using advanced Internet programming, and informed by focus groups with dentists, dental hygienists, and dental assistants we will develop DentalTobaccoControl.Net (DTC.Net) to deliver the intervention. The intervention will include case-based training, online opinion leader statements, a downloadable tobacco cessation toolbox, an "Ask the Expert" function, and a "collaboratory" where dental providers can communicate. DTC.Net will be available for 24 months, with updates and email reminders. In our RCT, we will test Hypothesis 1: The proportion of patients receiving provider tobacco cessation counseling will be greater in dental practices randomized to DTC.Net, compared with controls. Hypothesis 2: The proportion of tobacco using patients who quit will be greater in those enrolled from intervention dental practices compared with those at controls. We will recruit 100 practices from the Alabama Dental Practice Research Network, a unique, state-wide network of community-based dental practices; and survey patients with brief exit cards at time of dental visit. Fifty practices will be randomized to the DTC.Net intervention, and fifty to a control continuing dental education website unrelated to smoking. We will obtain the exit cards, assessing provider counseling behavior, from cohorts of unique patients, at 2, 8, 14, and 26 months after practice enrollment (Hypothesis 1). We will contact for follow-up telephone survey at 6 and 12 months after exit cards a random sample of 40 patients per practice, to assess tobacco quit rates (Hypothesis 2). Significance: By combining rigorous methodology, state-of-the-art technology, an experienced research team, and a unique community-based dental network, we will advance our understanding of tobacco control through dental practice and provide clinicians with an innovative and easily replicable approach to tobacco control.